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Climate change raises new risk: Are inland bridges too low?

This April 6, 2017 photo shows Milwaukee's South Sixth Street Bridge over the Kinnickinnic River. The Milwaukee Metropolitan Sewerage District raised the bridge to prevent the waterway from backing up amid downpours. It's a technique cities nationwide are using as officials prepare for more intense rainstorms resulting from a warming climate. (AP Photo/Ivan Moreno)

Milwaukee’s South Sixth Street Bridge over the Kinnickinnic River, as it looked on April 6. The Milwaukee Metropolitan Sewerage District has raised the bridge to prevent the waterway from backing up amid downpours. It’s a change that cities throughout the country are making to prepare for the intense rainstorms that have resulted from the planet’s having a warming climate. (AP Photo/Ivan Moreno)

Associated Press

DES MOINES, Iowa (AP) — A century-old train trestle stands as one of the trophies of Des Moines’ push to spruce up its downtown. Bicyclists and pedestrians pose for pictures beside the brightly painted beams of the Red Bridge and gather on viewing platforms overlooking the Des Moines River.

But hardly a decade after that restoration, the span was hoisted 4½ feet higher, at a cost of $3 million. That work came in response to experts’ conclusion that the river’s flooding risk was nearly double previous estimates.

The likely culprit? Climate change.

“It was like a bomb was dropped off in our lap,” Pam Cooksey, Des Moines city engineer, said of the revised flood forecasts from the Army Corps of Engineers.

The findings suggested that the bridge could act as a dam during bad storms, sending waves of backed-up floodwater into the refurbished business district.

Climate change is often seen as posing one of the greatest threats now looming over coastal areas. But the risks don’t stop there. Officials in inland cities also have much to worry about, including more intense storms and more frequent flooding. Even as President Donald Trump has announced plans for the U.S. to withdraw from a global climate agreement, many river cities are responding to climate change by raising or replacing bridges that suddenly seem too low to stay safely above water.

Milwaukee has seen various bridges raised as part of $400 million worth of flood-management projects that have been undertaken throughout the metropolitan area. A bridge over the Kinnickinnic River, for instance, was hoisted by the Milwaukee Metropolitan Sewerage District to prevent the waterway from backing up amid downpours.

Nationally, the reconstructed bridges range from multi-lane structures that handle heavy traffic loads to small rural spans traversed by country school buses and farmers who are shuttling between their fields. Bridges are being raised even in states such as Texas, where political leaders have long questioned whether climate change is real.

In Reno, Nevada, officials spent about $18 million to replace a bridge over the Truckee River last year and now plan to replace three more after flood-danger projections were increased by up to 15 percent.

Because the affected cities are inland, “A lot of these are not the kind of places that people are used to thinking of being in the forefront of climate change,” said Jim Schwab, manager of the Hazards Planning Center at the American Planning Association, which is working with nearly a dozen cities on flood-mitigation plans.

Many communities are “still feeling their way through this particular problem,” he said.

No one tracks how many cities are raising bridges or replacing them with taller ones. But the Federal Emergency Management Agency says it’s now routinely providing money for this purpose, although it could not say exactly how much. Typically, more than 1,500 bridges are rebuilt every year.

Schwab said he’s sure hundreds and possibly thousands of bridge-raising projects have been completed recently or are planned. A cursory check by the AP in a handful of states found at least 20 places where bridges have been raised or construction will begin soon.

FEMA is now finishing up a rule that states that floods “are expected to be more frequent and more severe over the next century due in part to the projected effects of climate change.” That could mean higher costs for a country that sustained more than $260 billion in flood damage between 1980 and 2013.

Given the Trump administration’s skepticism of climate change, however, a FEMA spokeswoman says the agency “has not determined what its next action will be” on the rule. The Corps of Engineers did not respond to requests for information on cities where flood risks have been reassessed.

As global temperatures have risen by more than 1.5 degrees on average since 1880, humidity has likewise increased. One result has been a corresponding increase in the intensity of downpours, according to David R. Easterling, director of the national climate assessment unit at the National Oceanic and Atmospheric Administration.

“It causes day after day of rainfall, and that leads to flooding,” Easterling said.

In some cases, a city’s likelihood of seeing what once would have been deemed a 100-year flood has doubled from what it was 40 years ago. According to the standard definition, a 100-year flood is the worst flood that can be expected to happen in a given century-long period. It has a 1 percent chance of occurring in any year.

In Cedar Rapids, Iowa, river-level forecasts have been increasing since 2008, when tropic-like rainstorms caused the normally placid Cedar River to climb higher than anyone had thought possible. In the end, the storm saw the city’s previous flood record topped by 11 feet. More than 1,100 blocks in Iowa’s second-largest city wound up underwater.

Afterward, the Corps of Engineers raised Cedar Rapids’ projections concerning the likelihood of a 100-year flood by 8 percent. As part of a massive flood-control project, the city decided to raise its Eighth Avenue Bridge by 14 feet, putting it 28 feet above the average water surface.

“What used to be the norm is no longer the norm,” said Rob Davis, the city’s flood-control program manager. “The norm is much higher.”

Elsewhere, the college town of Iowa City plans to add about 5 feet of clearance with a new bridge over the Iowa River. Similar projects are planned in Hobart, Indiana, and Rockford, Illinois, where higher river levels have been projected.

The preparations for climate change seem oddly disconnected from current political debates.

In Texas, where politicians including Sen. Ted Cruz have questioned whether the climate is growing warmer and if humans have caused the change, Austin has raised two bridges in the past five years and made plans to improve three more stream crossings, said Pam Kearfott, a supervising engineer in the city’s watershed protection department.

Officials “try to stick to the technical basis for change” and ignore the politics, she said.

Sterling Burnett, a research fellow at the Heartland Institute, a think tank that promotes skepticism about human-caused climate change, said the new flooding predictions and climate outlook could be exaggerated. Still, he doesn’t begrudge local governments for raising bridges and making other preparations.

“They have to work with the data given to them and make decisions,” Burnett said.

In the West, small communities in the Ross Valley north of San Francisco anticipate worse seasonal flooding from climate change. They plan to replace five bridges that are now too low, at a cost of more than $10 million.

As Cooper Martin, who heads the National League of Cities’ Sustainable Cities Institute, puts it, “With the changing climate, cities have to do something.”

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